Middle to late Miocene development of the equatorial Pacific high-productivity belt : a high time-resolution analysis of changes in diatom absolute abundances and sedimentation /
In the equatorial Pacific, the upwelling of nutrient-rich water causes high plankton productivity along an east-west belt overlying the equator. This region of high surface water productivity is reflected by an underlying lens of pelagic sediment accumulation, present since at least the Eocene. The...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743273581&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | In the equatorial Pacific, the upwelling of nutrient-rich water causes high plankton productivity along an east-west belt overlying the equator. This region of high surface water productivity is reflected by an underlying lens of pelagic sediment accumulation, present since at least the Eocene. The purpose of this study was to examine the development of the equatorial Pacific high-productivity belt from 14.5 to 9.5 Ma at a time resolution of 5 k.y. to 20 k.y. using three Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) sites (Sites 574, 572 and 844). Changes in carbonate and opal mass accumulation rates and diatom absolute abundances were analyzed. Results indicate that the time interval between 14.5 and 14.0 Ma was marked by an increase in diatom productivity in the eastern equatorial Pacific. Evidence includes an increase in opal and carbonate mass accumulation rates at Sites 572 and 844 and an increase in diatom absolute abundances at Sites 572 and 844. This increase in surface water productivity began at the same time as a global increase in benthic foraminiferal 6110. Its most likely cause was a strengthening of latitudinal thermal gradients resulting from east Antarctic ice sheet expansion. A second increase in diatom productivity occurred between 12.5 and 12.0 Ma. It was associated with increased opal mass accumulation rates at Site 844 and numerous diachronous diatom first and last occurrences between 13.0 and 12.0 Ma. Evidence suggests this event may in part be related to a localized reorganization of surface water circulation. Between 11.0 and 10.65 Ma, diatom assemblages at all sites are dominated by species of Thalassionema nitzschioides and Nitzschia porteri. About 10.6 Ma, Denticulopsis hustedtii replaces Nitzschia porteri at all sites, indicating an expansion of cooler water into the central equatorial Pacific. After 10.6 Ma, increases in Thalassiothrix longissima and Denticulopsis hustedtii are associated with increased J"O at Site 574. Many complex events may be responsible for the observed changes, including variable Northern Component Water production, shoaling of the Panama Isthmus, and initiation of the Equatorial Undercurrent. |
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| Item Description: | Vita. "Major Subject: Geology". |
| Physical Description: | xxii, 304 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |